Computational protocol: Reduced Amygdala and Ventral Striatal Activity to Happy Faces in PTSD Is Associated with Emotional Numbing

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Protocol publication

[…] Pre-processing and statistical analysis of fMRI data was conducted using Statistical Parametric Mapping (SPM-2, Wellcome Department of Neurology, London, UK). Functional scans were realigned, unwarped, spatially normalized and smoothed in order to remove movement artefact and to place data into a common anatomical frame. Images were normalized into standardized MNI space and smoothed using a Gaussian kernel (FWHM: 8 mm).An HRF-convolved boxcar model with temporal derivative was created to correspond to the experimental model, and a high pass filter was applied to remove low frequency fluctuations in the BOLD signal. Individual contrast images (fear versus neutral) were brought to the second level and examined using t-tests.For the group voxelwise analysis, random effects independent samples t-tests comparing the PTSD and Trauma Control group to happy (-neutral) faces were conducted. To test our a priori hypotheses, analyses were undertaken using a search region of interest (ROI) approach which included regions of the amygdala and ventral striatum (caudate and putamen, including nucleus accumbens). Search regions were defined by the Automated Anatomical Labelling (AAL) Masks and selected using the WFU Pickatlas (Version 1.02). We created an anatomical region of interest mask for the ventral striatum by combining caudate and putamen (including nucleus accumbens). Nucleus accumbens was identified at the inferior junction between the head of caudate and putamen, in accordance with previous studies and the Human Brain Atlas , . Coordinates of peak activations within the nucleus accumbens were confirmed with reference to the Human Brain Atlas.Previous studies of facial emotion processing have used an uncorrected p value of p<.05 for determining significant activations in small structures based on a priori hypotheses , or p<.005 when examining ventral striatum in monetary incentive tasks . Given our a priori directional hypotheses, in line with previous literature , we employed independent samples t-tests using the above ROIs, with an alpha value of p<.005, and a spatial extent threshold of 10 contiguous voxels. To examine the influence of comorbid depression, a sub-analysis (using the same analysis techniques as above) was conducted comparing PTSD_with depression (nā€Š=ā€Š15) and Trauma Controls, PTSD_no depression (nā€Š=ā€Š8) and Trauma Controls, and PTSD_with and PTSD_No depression groups using independent samples t-tests.For the correlational analysis, intensity beta values were extracted from the most significant voxels for each individual in the ventral striatum ROI. Pearson Product moment correlations were conducted in SPM2 within the PTSD group between each individual's peak BOLD ventral striatal activity in response to happy faces and their emotional numbing score (derived from ratings on the CAPS in a procedure taken from Foa et al., (1995). To control for PTSD severity, depression and state anxiety, correlations were conducted with PTSD severity (total CAPS score), DASS depression score, and DASS anxiety score included as covariates. A probability estimate of p<.01 and the extent threshold >10 voxels per cluster was adopted. […]

Pipeline specifications

Software tools SPM, AAL
Application Magnetic resonance imaging
Organisms Homo sapiens